There are two major conflicts running through "X-Men: First Class." One is interesting, though we’ve seen it before, and one is near-fatal to the film.

The first conflict is the ideological loggerheads between two powerful mutants — Charles Xavier (James McAvoy), a telepath, and Erik Lehnsherr (Michael Fassbender), who can manipulate metal with his mind. Charles is aware that normal humans hate and fear mutants, but wants to help humans anyway. Erik is likewise aware, but gradually decides that he would rather not. The second conflict is one of tone. X-Men: First Class, set during the early ’60s leading up to the Cuban Missile Crisis, breathes heavily about matters of major historical import — Erik as a boy survived Auschwitz — but also wants to be a poppy summer-fun blast in which mutants sprout wings or blue fur and flit around the sky like fireflies at dusk.

The result is a weird and unstable experience, and I wish I could say I gave in to the lightweight escapism. But when you present me with the Final Solution and the spectre of nuclear annihilation — which actually almost happened, with or without mutants — I have a hard time switching gears for the goofball scenes of young mutants in training, roughhousing with their budding powers. I don’t mean to be a killjoy; I just mean to say that historical high seriousness and retro pulp don’t blend well — you can see the seams. The first two X-Men films, directed by Bryan Singer, took themselves seriously — gloomily so, at times — but at least felt consistent. The stakes were high, and Singer, an openly gay director, plumbed the metaphor of mutants as persecuted homosexuals, but when the action beats came they felt rooted in something personal. Here, the historical import seems like a tacky backdrop for tackier action.

Charles and Erik (who will later triumphantly assume the dorky name “Magneto,” snarkily given to him by Jennifer Lawrence’s shape-shifting Mystique) enter into an increasingly uneasy alliance when Erik’s old foe from the Auschwitz days, Sebastian Shaw (Kevin Bacon), plans to use his own mutant powers and mutant minions to provoke nuclear war between the U.S. and Russia. The resulting radiation will kill off all the humans and empower the mutants. So Charles and Erik build their own team, made up mostly of disaffected youngsters with strange powers; perhaps significantly, perhaps not, of the two mutants of color, one dies early on and one turns to evil.

Michael Fassbender emerges as a cool, 007-like presence, the only real adult in the movie; James McAvoy seems to keep himself amused. For the most part, though, the large cast gets lost in the bombast, and January Jones as Shaw’s telepathic right-hand woman Emma Frost gives yet another dead-eyed performance in which she seems to be reading her lines phonetically. The director (and one of four named writers) of X-Men: First Class is credited as Matthew Vaughn, which I find hard to believe. Can this be the same man who gave us last year’s sarcastic, taboo-breaking superhero satire Kick-Ass (not to mention the enchanting comedy Stardust)? This film is a complete regression for Vaughn, who seemed to be forging a career as one of the few iconoclasts working in big Hollywood movies. There’s more outlaw excitement in any of Hit Girl’s scenes from Kick-Ass than in all of X-Men: First Class.

Save for a few hairdos and JFK on the tube, the ’60s milieu isn’t very convincing; the movie itself, meanwhile, feels as though it were made in 1996 or even 1986. A lot of that is due to Henry Jackman’s painfully cheesy score, but part of it is down to Matthew Vaughn’s passionless, visionless direction. Vaughn was supposed to direct 2006’s X-Men: The Last Stand but dropped out two weeks before filming started; did he take this movie on to prove he could’ve done better with the earlier film, or did he forget in the intervening five years why he’d wanted to make an X-Men film in the first place?

"X-Men: First Class" has been getting something of a free ride from the fanboy press, who respect Vaughn for his past films and are grateful that someone tried to make a better movie than "The Last Stand" and the oafish "Wolverine." But loyalty to a director and relief that a film doesn’t stink on ice aren’t enough reason to excuse mediocrity.